Rabi oscillations and stimulated mode conversion on the subwavelength scale.

We study stimulated mode conversion and dynamics of Rabi-like oscillations of weights of guided modes in deeply subwavelength guiding structures, whose dielectric permittivity changes periodically in the direction of light propagation. We show that despite strong localization of the fields of eigenmodes on the scales below the wavelength of light, even weak longitudinal modulation couples modes of selected parity and causes periodic energy exchange between them, thereby opening the way for controllable transformation of the internal structure of subwavelength beams. The effect is reminiscent of Rabi oscillations in multilevel quantum systems subjected to the action of periodic external fields. By using rigorous numerical solution of the full set of the Maxwell's equations, we show that the effect takes place not only in purely dielectric, but also in metallic-dielectric structures, despite the energy dissipation inherent to the plasmonic waveguides. The stimulated conversion of subwavelength light modes is possible in both linear and nonlinear regimes.